docs: def delete_dependency(self, from_task_name, to_task_name):
          """ Delete a dependency between two tasks. """
  
          logger.debug('Deleting dependency from {0} to {1}'.format(from_task_name, to_task_name))
          if not self.state.allow_change_graph:
              raise DagobahError("job's graph is immutable in its current state: %s"
                                 % self.state.status)
  
          self.delete_edge(from_task_name, to_task_name)
          self.commit()